1. Field of the Invention
The present invention relates to an electron tube in which a side tube and input faceplate are fixed together by a sealing metal, such as a metal containing predominately indium, which metal is maintained at a temperature below the its melting point, such as room temperature.
2. Description of the Prior Art
One conventional electron tube manufactured according to a cold indium method is described in Japanese Laid-Open Patent Publication (Kokai) No. HEI-4-58444. In this method, the side tube and input faceplate are placed within a vacuum device referred to as a transfer device and connected via indium, which is maintained below its melting point (for example, room temperature) and used in its solid state. When joining the side tube and input faceplate, the input faceplate is pressed against the side tube, deforming the indium. Hence, pressing indium between the side tube and input faceplate achieves a vacuum air-tight seal for the electron tube. Other examples applying to electron tubes manufactured using this cold indium method are described in Japanese Laid-Open Patent Publication (Kokai) Nos. SHO-57-136748, SHO-54-16167 and SHO-61-211941.
Examples of an electron tube manufactured according to a hot indium method are described in Japanese Laid-Open Patent Publication (Kokai) Nos. HEI-6-318439 and HEI-3-133037. In this method, the side tube and input faceplate are joined within the transfer device using indium that has been melted in a heater. An indium collecting depression is provided in the side tube to prevent the melted indium from flowing out of the side tube.
However, various problems occur with electron tubes constructed using the cold indium method described above. For example, since the end face of the side tube is formed approximately flat and parallel to the inner surface of the input faceplate, even if the side tube and input faceplate are pressed with great force against the indium, a good airtight seal with the indium cannot always be achieved, because the surfaces contacting the indium do not conform well with each other. Further, the indium protrudes outwardly of the contacting surfaces when the input faceplate is pressed against the side tube. Hence, problems with airtightness can occur in these electron tubes, which require sufficiently good airtightness. Due to this poor airtightness, oxygen and moisture from the air can enter the electron tube, degrading the sensitivity of the photocathode. The seal formed with indium is particularly bad when the end of the side tube is formed of a metallic material.